Question
A 48-year-old woman who rarely goes outdoors is brought by her family due to months of diffuse bone discomfort, especially in the back and thighs. She also reports weakness and has difficulty rising from a chair. On examination, there is tenderness over long bones and a waddling type of walk.
What is the most likely diagnosis?
a. Early bone density loss (osteopenia)
b. Generalized bone fragility without pain (osteoporosis)
c. Defective bone mineralization in adults
d. Abnormal bone remodeling disorder (Paget disease)
e. Vitamin C deficiency
Answer
Defective bone mineralization in adults (Osteomalacia)
Detailed Explanation
This is a classic presentation of Osteomalacia.
Key Clinical Clues
- Bone pain + tenderness → hallmark
- Proximal muscle weakness → difficulty standing, climbing stairs
- Waddling gait → very characteristic
- Low sunlight exposure → vitamin D deficiency
Pathophysiology
- Vitamin D deficiency → ↓ calcium & phosphate absorption
- → defective mineralization of osteoid
- → soft bones (NOT brittle bones)
Why NOT other options?
- Osteoporosis / Osteopenia
- Bone density ↓
- Usually asymptomatic until fracture
- No muscle weakness or waddling gait
- Paget disease
- Disorganized bone remodeling
- Features: skull enlargement, hearing loss
- Not proximal myopathy
- Scurvy
- Vitamin C deficiency
- Features: bleeding gums, petechiae, poor wound healing
Investigations (Very High-Yield)
- ↓ Vitamin D
- ↓ Calcium (sometimes normal)
- ↓ Phosphate
- ↑ ALP (almost always ↑)
- X-ray: Looser’s zones (pseudofractures)
Cheat Sheet (Exam Gold)
- Osteomalacia = soft bones (vitamin D deficiency)
- Key triad:
- Bone pain
- Proximal myopathy
- Waddling gait
- Labs:
- ↓ Vit D, ↓ PO₄, ↑ ALP
- X-ray: Looser zones
- Risk factors:
- Low sunlight
- Malabsorption
- CKD
Flash Cards
Q1: Most characteristic gait in osteomalacia?
A: Waddling gait
Explanation: Due to proximal muscle weakness
Q2: Key difference: osteomalacia vs osteoporosis?
A: Osteomalacia → pain + weakness; osteoporosis → silent
Q3: Most consistent lab finding?
A: Raised ALP
Q4: Cause of osteomalacia?
A: Vitamin D deficiency
Q5: X-ray finding?
A: Looser’s zones (pseudofractures)
MCQs
1. A patient with diffuse bone pain and proximal muscle weakness most likely has:
a. Osteoporosis
b. Osteomalacia
c. Osteopenia
d. Rheumatoid arthritis
Answer: b
Explanation: Pain + proximal myopathy → osteomalacia
2. Which of the following is FALSE regarding osteomalacia?
a. Causes bone pain
b. Causes proximal muscle weakness
c. Always presents with fractures first
d. Associated with vitamin D deficiency
Answer: c
Explanation: Symptoms precede fractures
3. Most consistent biochemical abnormality?
a. Low ALP
b. High calcium
c. High ALP
d. High sodium
Answer: c
Explanation: ↑ ALP due to increased osteoblastic activity
4. Which feature best differentiates osteomalacia from osteoporosis?
a. Fractures
b. Bone density
c. Bone pain and muscle weakness
d. Age group
Answer: c
Explanation: Osteoporosis is silent
5. Which of the following is FALSE?
a. Osteomalacia causes soft bones
b. Osteoporosis causes brittle bones
c. Osteomalacia is due to vitamin D deficiency
d. Osteoporosis causes proximal myopathy
Answer: d
Explanation: Proximal myopathy is osteomalacia feature
6. A patient with waddling gait and low sunlight exposure most likely has:
a. Paget disease
b. Scurvy
c. Osteomalacia
d. Osteoarthritis
Answer: c
Explanation: Classic exam vignette
Summary for Quick Exam Revision
Osteomalacia is a disorder of defective bone mineralization due to vitamin D deficiency, leading to soft bones. It presents with diffuse bone pain, tenderness, and proximal muscle weakness, often causing a waddling gait—this combination is highly characteristic and frequently tested in exams. Unlike osteoporosis, which is typically asymptomatic until fractures occur, osteomalacia produces significant symptoms early. Risk factors include poor sunlight exposure, malabsorption, chronic kidney disease, and certain medications. Laboratory findings usually show low vitamin D, low phosphate, and elevated alkaline phosphatase, while calcium may be low or normal. Radiologically, Looser’s zones or pseudofractures are classic. The key exam takeaway is: bone pain plus proximal myopathy equals osteomalacia until proven otherwise.